1. Field of the Invention:
The present invention relates to a direct drive type rotation dividing table for positioning by rotating the dividing table by a predetermined angle by a direct driving method without using a reduction gear device and, in particular, to a direct drive type rotation dividing table in which, even when a large load is applied to the table, the table can be securely supported by increasing a clamping force at the time of positioning of the dividing table.
2. Description of the Art:
In a direct drive type rotation dividing table which does not use a reduction gear mechanism, backlash and noise due to a reduction gear are not generated and torsional rigidity can be increased by disposing a clamp mechanism close to a table rotation shaft. Thus, there are advantages in that a torsional deformation of the dividing table shaft can be prevented when a cutting load is applied to a work and machining accuracy can be improved. A prior art direct drive type rotation dividing table of this type, for example, was previously proposed by the inventor of the present application in Japanese Utility Model Laid-open Publication Hei 1-121636. In this rotation dividing table, a motor stator is fixed in a housing and a motor rotor is disposed coaxially with the motor stator. The motor rotor has an output shaft rotatably supported by the housing through a bearing. The dividing table is coupled to the output shaft. Within the housing, there are also provided a rotation detector for detecting a rotation angle of the dividing table and a clamp mechanism for holding the dividing table at a stopped position.
The clamp mechanism includes a clamping member secured to a free end of an elastic body which is fixed to the housing in a cantilever fashion so that the clamping member is brought into contact with or moved away from the output shaft, a cylinder having a plane portion and slidably mounted on the housing for movement in an axial direction, and a piston having a plane portion opposing to the cylinder and movable in the axial direction while sliding in the cylinder.
When the motor stator is energized, the motor rotor and the output shaft are rotated by a predetermined angle to perform a dividing of the dividing table. Thereafter, the dividing table is clamped. At this time, pressurized fluid is supplied to a space between opposing plane portions of the cylinder and the piston of the clamp mechanism so that the cylinder is slidingly moved to strongly pressed the clamping member to the output shaft against the elasticity of the elastic body. At the same time, the piston abuts a backside of the dividing table and applies force in a direction opposite to the direction of the clamping force. By such an arrangement, an unnecessary thrust force is prevented from being applied to the bearing of the output shaft during the clamping operation.
However, in this prior art direct drive type rotation dividing table, a friction surface which contributes to the clamping is only provided on the clamping member, and the pressure of the pressurized fluid contributes only an imparted pressure which is loaded to the cylinder. The pressure loaded to the piston cancels out the thrust force applied to the bearing of the output shaft and does not contribute to the clamping force. As a result, it is difficult to obtain a large clamping force.
Furthermore, a clamping member and a large coil spring or the like to return the piston to the original position is necessary and, thus, the number of parts and costs are increased.
Moreover, since the prior art dividing table is constructed so that the piston is moved while by being supported by a slide guide, the abutting of the upper surface of the piston against the backside of the dividing table and the distribution of the pressing force are not uniform. As a result, another problem is encountered in that a minute inclination of the dividing table is apt to be caused.